Restrict Agent FFmpeg tools to read-only inspection

[LittleLaXerath]

中文

更新内容

• 将 Agent 可见的 FFmpeg 工具限制为 ffmpeg_probe 与 ffmpeg_loudness_analyze 两个只读操作。
• 移除 Agent 对 ffmpeg_prepare_audio 和 ffmpeg_loudness_normalize 的定义与执行路由，避免对话模型未经确认写入音频文件。
• 保持 C ABI 与四个白名单 FFmpeg 操作不变；音频准备和响度标准化继续提供给 pi-desktop，由桌面界面展示计划并取得用户确认。
• 保持组件安装、更新、卸载为仅用户触发的生命周期操作。
• 增加精确权限边界测试，并更新 README、组件契约和中英文 CHANGELOG.md。

验证

• Rust 工作区：57 项测试通过，2 项按设计忽略。
• Clippy：-D warnings 通过。
• 本机真实 FFmpeg：四个白名单操作全部通过。

English

Changes

• Limit the Agent-visible FFmpeg surface to the read-only ffmpeg_probe and ffmpeg_loudness_analyze tools.
• Remove Agent definitions and execution routes for ffmpeg_prepare_audio and ffmpeg_loudness_normalize, preventing unconfirmed audio-file writes by the conversational model.
• Preserve the stable C ABI and all four allow-listed FFmpeg operations; preparation and normalization remain available to pi-desktop, where the user can review and confirm the action.
• Keep component install, update, and uninstall strictly user-triggered.
• Add exact permission-boundary coverage and update the README, component contract, and bilingual CHANGELOG.md.

Validation

• Rust workspace: 57 tests passed, 2 intentionally ignored.
• Clippy passed with -D warnings.
• All four allow-listed operations passed against a real local FFmpeg build.